It is known from the prior art to apply thin layers and films to a substrate using many techniques, for example printing and screen-printing. Inkjet and laser printers will also produce thin films of ink.
It is known to use jet printing techniques to form three dimensional objects; for example in U.S. Pat. Nos. 5,059,226 and 5,140,937 there is disclosed the direct jetting of curable materials onto a substrate. In WO 97/48557 and WO 99/19900, there is described a method of forming three dimensional features on a surface using successive drops of inkjetted material to build up a deposit. The deposit is generally built up vertically to produce three dimensional objects, for example Braille characters and multi-layer optical and electrical devices.
Plastic layers and films capable of controlling electromagnetic radiation are important. U.S. Pat. No. 6,024,455 demonstrates the application of such plastic materials. The method described involves the melt co-extrusion of two (isotropic) polymers to produce a laminate film made up of hundreds of thin, alternating, layers of the two polymers. The layers are 0.1 μm thick or thinner.
To achieve controlled final optical properties, it is essential that the layers are dimensionally precise in the micro and macro dimensions, as well as optically clear.
Careful choice of the polymers gives control of light absorption, transmittance and reflection. High speed film web formation from the method described in U.S. Pat. No. 6,024,455 is clearly possible. However, it is difficult with this method to vary, readily the macro, micro and nano properties within each layer and between each layer.
The alignment of liquid crystal phases is usually brought about by a polyamide alignment layer that is in contact with the liquid crystals; U.S. Pat. No. 5,539,074. U.S. Pat. No. 5,567,349 and U.S. Pat. No. 5 593 617 disclose forming the alignment layer by polymerisation under polarised light of a layer that has been applied by spin coating. EP 1 227 347 discloses a process of jet printing an alignment layer followed by depositing a layer of cross-linkable liquid crystal in a volatile diluent.
U.S. Pat. No. 5,855,836 discloses a hot-melt system, in which a solid formulation is heated until it melts and is jet dispensed in a desired pattern on to a substrate. It then cools and solidifies, and the sequence is repeated to build a 3-dimensional object. The formulation includes a reactive component which is finally activated to cure the object. Since wax like materials are used, the formed layers are opaque and this method forms thick layers, e.g. 50 μm. Another disadvantage here is that the materials available are extremely limited. A related process is described in U.S. Pat. No. 5,059,266 and U.S. Pat. No. 5,140,937 involving direct jetting of curable materials. This is used for forming shaped 3 dimensional objects and not films.
It is also known to use red, green and blue filters in liquid crystal displays, which are deposited by jetting suitable pigments contained in suitable binders and solvents into a well.
One common feature with the prior art techniques is that the dispensed droplets of liquid are directed onto specific locations on a substrate so that the droplets adhere to the substrate in substantially the precise areas that the droplets land in order that the resulting deposit produces an image or print with as high (fine) a resolution as possible. This makes it hard to form a layer of substantially uniform thickness. In addition, when resins or curable resins are jet deposited they are generally supported in a volatile diluent.
There is an emerging need to produce on demand thin films made up of resins having active functionality for various purposes. For example: some polymeric resins have an active property, which may for example be physical, chemical, optical, electro-optical, magnetic or electrical (e.g. birefringence/wave guiding effects from liquid crystalline resins), or light emitting effects from organic/inorganic light emitting resins, electrical conducting effects from conducting resins. In particular, the capability to vary and integrate a variety of such active resins, in their active state (i.e. as tracks or patterns or circuits), within a layerwise plastic frame around the active resin is contemplated to be important in the future. In particular forming the active resin from suitable monomeric, oligomeric (pre-polymers) resin mixtures would allow greater flexibility in controlling the final active properties required.
In the field of security printing, the art is looking for new methods of creating authenticating materials that cannot be reproduced unlawfully and yet can readily be verified. Having these security features embedded within thin layers of polymeric material(s) would yield unusual effects in addition to the effects from the layering structure
U.S. Pat. No. 5,945,463 and U.S. Pat. No. 6,277,929 disclose a photocurable resin composition comprising a high molecular weight resin and a curable diluent that can be extruded to form a thick layer approx. 1 mm thick that is then photocured.